Memory controllers, memory systems, solid state drives and methods for processing a number of commands

ABSTRACT

The present disclosure includes methods and devices for a memory controller. In one or more embodiments, a memory controller includes a plurality of back end channels, and a command queue communicatively coupled to the plurality of back end channels. The command queue is configured to hold host commands received from a host. Circuitry is configured to generate a number of back end commands at least in response to a number of the host commands in the command queue, and distribute the number of back end commands to a number of the plurality of back end channels.

PRIORITY INFORMATION

This application is a Divisional of U.S. application Ser. No. 14/268,125filed May 2, 2014, which is a Divisional of U.S. application Ser. No.13/796,851 filed Mar. 12, 2013, now U.S. Pat. No. 8,751,700, which is aDivisional of U.S. application Ser. No. 13/599,594 filed Aug. 30, 2012,now U.S. Pat. No. 8,396,995, which is a Divisional of U.S. applicationSer. No. 13/242,535 filed Sep. 23, 2011, now U.S. Pat. No. 8,260,973,which is a Divisional of U.S. application Ser. No. 12/421,093 filed Apr.9, 2009, now U.S. Pat. No. 8,055,816, the specifications of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor memorydevices, methods, and systems, and more particularly, to memorycontrollers, memory systems, solid state drives and methods forprocessing a number of commands.

BACKGROUND

Memory devices are typically provided as internal, semiconductor,integrated circuits in computers or other electronic devices. There aremany different types of memory including volatile and non-volatilememory. Volatile memory can require power to maintain its data andincludes random-access memory (RAM), dynamic random access memory(DRAM), synchronous dynamic random access memory (SDRAM), among others.Non-volatile memory can provide persistent data by retaining storedinformation when not powered and can include NAND flash memory, NORflash memory, read only memory (ROM), electrically erasable programmableROM (EEPROM), erasable programmable ROM (EPROM), and phase change randomaccess memory (PCRAM), among others.

Memory devices can be combined together to form a solid state drive(SSD). An SSD can include non-volatile memory, e.g., NAND flash memoryand NOR flash memory, and/or can include volatile memory, e.g., DRAM andSRAM, among various other types of non-volatile and volatile memory.

An SSD can be used to replace hard disk drives as the main storagedevice for a computer, as the SSD can have advantages over hard drivesin terms of performance, size, weight, ruggedness, operating temperaturerange, and power consumption. For example, SSDs can have superiorperformance when compared to magnetic disk drives due to their lack ofmoving parts, which may improve seek time, latency, and otherelectro-mechanical delays associated with magnetic disk drives. SSDmanufacturers can use non-volatile flash memory to create flash SSDsthat may not use an internal battery supply, thus allowing the drive tobe more versatile and compact.

An SSD may include a number of memory devices, e.g., a number of memorychips (as used herein, “a number of” something can refer to one or moresuch things; e.g., a number of memory devices can refer to one or morememory devices). As one of ordinary skill in the art will appreciate, amemory chip may include a number of dies. Each die may include a numberof memory arrays and peripheral circuitry thereon. A memory array mayinclude a number of planes, with each plane including a number ofphysical blocks of memory cells. Each physical block may include anumber of pages that can store a number of sectors of data.

Memory systems, e.g., an SSD, may be incorporated into a computingsystem, the memory system can be communicatively coupled to a host by acommunication interface, e.g., a Serial Advanced Technology Attachment(SATA) high speed serial bus primarily designed for transfer of commandsand data between the host and mass storage devices, such as hard diskdrives, optical drives, and SSDs.

Commands, such as program commands, read commands, and erase commands,among other commands, may be used during operation of an SSD. Forexample, a program, e.g., write, command may be used to program data ona solid state drive, a read command may be used to read data on a solidstate drive, and an erase command may be used to erase data on a solidstate drive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a computing system, inaccordance with one or more embodiments of the present disclosure.

FIG. 2 is a functional block diagram of a computing system including atleast one memory system, in accordance with one or more embodiments ofthe present disclosure.

FIG. 3 is a functional block diagram of a memory system controllercommunicatively coupled to a number of memory devices, in accordancewith one or more embodiments of the present disclosure.

FIG. 4 illustrates a logical-to-physical address map, in accordance withone or more embodiments of the present disclosure.

FIG. 5 is a functional block diagram of a command queue of a front endDMA, in accordance with one or more embodiments of the presentdisclosure.

FIGS. 6A and 6B illustrate operation of a command queue of a front endDMA, in accordance with one or more embodiments of the presentdisclosure.

FIG. 7 is a flow diagram for distributing commands among a number ofback end channels, in accordance with one or more embodiments of thepresent disclosure.

FIG. 8 is a functional block diagram illustrating an interface between afront end and a number of channels, in accordance with one or moreembodiments of the present disclosure.

FIG. 9A is a functional block diagram of a Direct Memory Access module(DMA) Descriptor Block, implemented in accordance with one or moreembodiments of the present disclosure.

FIG. 9B illustrates an entry in the DMA Descriptor Block (DDB)illustrated in FIG. 9A, implemented in accordance with one or moreembodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure includes memory controllers, memory systems,solid state drives and methods for processing a number of commands. Inone or more embodiments, a memory controller includes a plurality ofback end channels, and a command queue communicatively coupled to theplurality of back end channels. The command queue can be configured tohold host commands received from a host. Circuitry is configured togenerate a number of back end commands at least in response to a numberof the host commands in the command queue, and distribute the number ofback end commands to a number of the plurality of back end channels.

The present disclosure also includes methods and devices for a memorycontroller. In one or more embodiments, a memory controller includes aplurality of back end channels, and a front end command dispatchercommunicatively coupled to the plurality of back end channels and acommand queue. The command dispatcher can be configured to determine anet change to memory to be accomplished by the number of commands, andto modify one or more of the number of commands in order to optimizedistribution of the number of commands among the plurality of back endchannels.

The figures herein follow a numbering convention in which the firstdigit or digits correspond to the drawing figure number and theremaining digits identify an element or component in the drawing.Similar elements or components between different figures may beidentified by the use of similar digits. For example, 104 may referenceelement “04” in FIG. 1, and a similar element may be referenced as 204in FIG. 2, etc.

FIG. 1 is a functional block diagram of a computing system, inaccordance with one or more embodiments of the present disclosure. Theembodiment of FIG. 1 illustrates the components and architecture of oneembodiment of a computing system 100. Computing system 100 includes amemory system 104, for example a solid state drive (SSD),communicatively coupled to a host, such as host 102, through aninterface 106, e.g., USB, PCI, SATA/150, SATA/300, or SATA/600interface, among others.

SATA was designed as a successor to the Advanced Technology Attachment(ATA) standard, which is often referred to as Parallel ATA (PATA).First-generation SATA interfaces, also known as SATA/150 or unofficiallyas SATA 1, communicate at a rate of about 1.5 gigabits per second(Gb/s), or 150 megabytes per second (MB/s). Subsequently, a 3.0 Gb/ssignaling rate was added to the physical layer, effectively doubling themaximum, e.g., uppermost data throughput from 150 MB/s to 300 MB/s. The3.0 Gb/s specification, also known as SATA/300 or unofficially as SATAII or SATA2. SATA/300's transfer rate may satisfy magnetic hard diskdrive throughput requirements for some time; however, solid state drivesusing multiple channels of fast flash may support much higher datatransfer rates, so even faster SATA standards, e.g., SATA/600 having athroughput of 6 Gb/s, may be implemented in supporting flash solid statedrive read speeds.

The host 102 can include a number of separate integrated circuits, ormore than one component or function can be on the same integratedcircuit. According to one or more embodiments, the host 102 can bephysically implemented in a computing system 100, at least in part, as a“motherboard,” with the SSD 104 being physically implemented on aseparate card, the motherboard and SSD being communicatively coupledthrough a bus.

Host 102 can include a number of processors 105, e.g., parallelprocessors, co-processors, processor cores, etc., communicativelycoupled to a memory and bus control 107. The number of processors 105can be a microprocessor, or some other type of controlling circuitrysuch as an application-specific integrated circuit (ASIC). Othercomponents of the computing system may also have processors. The memoryand bus control 107 can have memory and other components directlycommunicatively coupled thereto, for example, dynamic random accessmemory (DRAM) 111, graphic user interface 113, or other user interface,e.g., display monitor, keyboard, mouse, etc.

The memory and bus control 107 can also have a peripheral and buscontrol 109 communicatively coupled thereto, which in turn, can connectto a number of devices, such as such as a flash drive 115 using auniversal serial bus (USB) interface, a non-volatile memory host controlinterface (NVMHCI) flash memory 117, or an SSD 104. As the reader willappreciate, a SSD 104 can be used in addition to, or in lieu of, a harddisk drive (HDD) in a number of different computing systems. Thecomputing system 100 illustrated in FIG. 1 is one example of such asystem.

FIG. 2 is a functional block diagram of a computing system including atleast one memory system, in accordance with one or more embodiments ofthe present disclosure. Computing system 200 includes a memory system204, e.g., a SSD, communicatively coupled to host 202. SSD 204 can becommunicatively coupled to the host 202 through an interface 206, e.g.,cable, bus, such as a SATA interface. SSD 204 can be analogous to thesolid state drive 104 in FIG. 1.

FIG. 2 illustrates the components of one or more embodiments of a solidstate drive 204, including a controller 210, a physical interface 208,e.g., a connector, and a number of memory devices 212-1, . . . , 212-N,a number of memory devices corresponding to a number of channels of thecontroller 210 (e.g., one or more memory devices corresponding to aparticular channel). Accordingly, memory devices 212-1, . . . , 212-Nare shown on the drawings as “channel No. memory.” As used herein, amemory device can include a number of memory cells, e.g., die, chip,array, or other group, that share control inputs, and may be fabricatedusing a number of memory types, e.g., NAND flash. Control inputs cangenerally include address latch enable (ALE), chip enable (CE), readenable (RE), ready/busy (R/B), write protect (WP), and input/output(I/O) connections such as pins, pads, or the like. In one or moreembodiments, the SSD 204 can include a housing to enclose the SSD 204,though such housing is not essential, for example, the host 202 and SSD204 may both be enclosed by a computing system housing.

The interface 206 can be used to communicate information between SSD 204and another device, such as a host 202. According to one or moreembodiments, SSD 204 can be used as a storage device in computing system200. According to one or more embodiments, SSD 204 can be configured asan external, or portable, memory system for computing system 200, e.g.,with plug-in connectivity.

The controller 210 can communicate with the memory devices 212-1, . . ., 212-N to operate, e.g., read, program (i.e., write), erase, etc., thememory cells of the memory devices. The controller 210 can be used tomanage communications with, and the data stored in, the memory devices212-1, . . . , 212-N. Controller 210 can have circuitry that can be anumber of integrated circuits. Controller 210 can also have circuitrythat can be a number of discrete components as well. For one or moreembodiments, the circuitry in controller 210 can include controlcircuitry for controlling access across a number of channels, and acrossa number of memory devices 212-1, . . . , 212-N. The memory controller210 can selectively communicate through the number of channels to thecorresponding memory device(s).

The communication protocol between the host 202 and the SSD 204 may bedifferent than what is required for accessing a memory device e.g.,memory devices 212-1, . . . , 212-N. Memory controller 210 can includecontrol circuitry configured to translate commands received from thehost 202 into appropriate commands to accomplish the intended operationacross the number of memory devices 212-1, . . . , 212-N. Circuitry ofthe memory controller 210 can provide a translation layer between thehost 202 and the SSD 204. Memory controller 210 can also process hostcommand sequences, the associated data, and other information, e.g.,signals, to appropriate channel command sequences, for example to storeand retrieve data. Memory controller 210 can selectively distributecommands, communicate (e.g., receive, send, transmit) associated data,and other information, through an appropriate channel to a correspondingmemory device at an appropriate time.

According to one or more embodiments of the present disclosure, eachmemory device 212-1, . . . , 212-N can include a number of memory cells.The memory devices 212-1, . . . , 212-N can be formed using varioustypes of volatile or non-volatile memory arrays, e.g., NAND flash, DRAM,among others. According to one or more embodiments of the presentdisclosure, the memory devices 212-1, . . . , 212-N can include a numberof flash memory cells configured in a NAND architecture, a NORarchitecture, an AND architecture, or some other memory arrayarchitecture, all of which may be used in implementing one or moreembodiments of the present disclosure.

Memory devices 212-1, . . . , 212-N can include a number of memory cellsthat can be configured to provide particular physical or logicalconfigurations, such as a page, block, plane, array, or other group. Apage can store data in accordance with a number of physical sectors ofdata. Each physical sector can correspond to a logical sector and caninclude overhead information, such as error correction code (ECC)information and logical block address (LBA) information, as well as userdata. As one of ordinary skill in the art will appreciate, logical blockaddressing is a scheme often used by a host for identifying a logicalsector of information. As an example, a logical sector can storeinformation representing a number of bytes of data, e.g., 256 bytes, 512bytes, or 1,024 bytes. As used herein, a page refers to a unit ofprogramming and/or reading, e.g., a number of cells, or portions of datastored thereon, that can be programmed and/or read together or as afunctional group. For example, some memory arrays can include a numberof pages that make up a block of memory cells, a block including memorycells which can be erased together as a unit, e.g., the cells in eachphysical block can be erased in a substantially simultaneous manner. Anumber of blocks can be included in a plane of memory cells. A number ofplanes of memory cells can be included on a die. An array can include anumber of die. By way of example, and not of limitation, a 128 Gb memorydevice can include 4314 bytes of data per page, 128 pages per block,2048 blocks per plane, and 16 planes per device. However, embodimentsare not limited to this example.

Each memory device 212-1, . . . , 212-N can include various types ofvolatile and non-volatile memory arrays, e.g., flash and DRAM arrays,among others. In one or more embodiments, memory devices 212-1, . . . ,212-N can be solid state memory arrays. Memory devices 212-1, . . . ,212-N can include a number of memory cells that can be grouped in units.As used herein, a unit can include a number of memory cells, such as apage, physical block, plane, an entire array, or other groups of memorycells. For example, a memory device can be a memory array and include anumber of planes, with each plane including a number of physical blocks.The memory cells in each physical block can be erased together as aunit, e.g., the cells in each physical block can be erased in asubstantially simultaneous manner. For example, the cells in eachphysical block can be erased together in a single operation. A physicalblock can include a number of pages. The memory cells in each page canbe programmed together as a unit, e.g., the cells in each page can beprogrammed in a substantially simultaneous manner. The memory cells ineach page can also be read together as a unit.

A physical sector of a memory system can correspond to a logical sector,and can include overhead information, such as error correction code(ECC) information and logical block address (LBA) information, as wellas user data. As one of ordinary skill in the art will appreciate,logical block addressing is a scheme often used by a host foridentifying a logical sector of information. As an example, eachphysical sector can store information representing a number of bytes ofdata, e.g., 256 bytes, 512 bytes, or 1,024 bytes, among other numbers ofbytes. However, embodiments of the present disclosure are not limited toa particular number of bytes of data stored in a physical sector orassociated with a logical sector.

FIG. 3 is a functional block diagram of a memory system controllercommunicatively coupled to a number of memory devices, in accordancewith one or more embodiments of the present disclosure. As shown in FIG.3, memory controller 310 can be communicatively coupled to a number of,e.g., eight, memory devices, e.g., 312-1, . . . , 312-N. In one or moreembodiments, the memory devices can be those shown at 212-1, . . . ,212-N in FIG. 2. Each memory device, e.g., 312-1, . . . , 312-N,corresponds to a channel, e.g., 350-1, . . . , 350-N, of the controller310. As used herein, a memory device can include a number of memorycells that share control inputs, as previously discussed. In one or moreembodiments, memory controller 310 can be an SSD controller. In one ormore embodiments, memory controller 310 can be analogous to controller210 shown in FIG. 2.

Each memory device, e.g., 312-1, . . . , 312-N, can be organized aspreviously described with respect to memory devices 212-1, . . . ,212-N, and can be fabricated on individual dies, or can be fabricated onstacked dies. Each die can include a number of arrays of memory cells.The memory controller 310 can include a front end portion 344 and a backend portion 346. The controller 310 can process commands and data in thefront end 344, e.g., to optimize distribution of the number of commandsamong the plurality of back end channels, such as by reducing thequantity of commands transmitted on to the back end portion 346. Thecontroller 310 can further process commands and data in each of the backend channels to achieve additional efficiency of memory operations withregard to a particular channel. In this manner, the controller 310manages communications with the memory devices 312-1, . . . , 312-N.

As shown in FIG. 3, the front end portion 344 can include a hostinterface 314 communicatively coupled to a task file 315 and a hostbuffer 322, e.g., FIFO, of an application layer 320. For example, thehost interface 314 can be configured to communicate input and outputinformation, e.g., data streams, with a host, e.g., 202 in FIG. 2,through the physical interface on an SSD, e.g., 208 in FIG. 2, and aSATA interface, e.g., 206 in FIG. 2. According to one or moreembodiments, a command (including the command parameters), e.g., acommand portion of the input information, can be directed to the taskfile 315, and an associated payload, e.g., a data portion of the inputinformation, can be directed to the host FIFO 322.

The task file 315 can be a one deep queue and can be in communicationwith a front end direct memory access module (DMA) 316 through a commandprocessor and dispatcher 318 (hereinafter “command dispatcher”). Commanddispatcher 318 is configured (e.g., includes hardware) such that it cancheck the command in the task file 315 on arrival from the host againstcertain criteria (e.g., integrity checking), and once verified withrespect to the criteria, can accept the arriving command, and candistribute it from the task file 315 to the front end DMA 316 and toappropriate back end channels. Previous approaches to integrity checkinghave been performed using firmware; however, performing host commandintegrity checking in hardware is faster, resulting in increased hostcommand processing speed by the command dispatcher 318.

The host FIFO 322 can be communicatively coupled to an encryption device324 having a number of encryption engines, e.g., encryption enginesimplementing an AES algorithm. The encryption device 324 may beconfigured to process, e.g., encrypt, a payload associated with aparticular command, and transmit the payload to the front end DMA 316.Additional detail on the operation of the encryption device 324 can befound in commonly assigned U.S. patent application Ser. No. 12/333,822,filed on Dec. 12, 2008, entitled “Parallel Encryption/Decryption”,having at least one common inventor, and having attorney docket number1002.0400001.

The front end portion 344 can also have a number of other processors330, which can include a front end processor (FEP) 328, memory 336,e.g., RAM, ROM, a DMA 332, and a main buffer 334. The number ofprocessors 330 can be communicatively coupled to the front end DMA 316,for example, by a communication bus.

The front end DMA 316 can include a DMA descriptor block (DDB) andregister 340, including associated registers, for containing a number ofwords of data. The front end DMA 316 can also include an arbiter 342 forarbitrating between a number of channels communicatively coupledthereto. The encryption device 324 can also be communicatively coupledto the FEP 328. The FEP 328 can also be communicatively coupled directlyto the host FIFO 322, and to the front end DMA 316.

The front end DMA 316 can be communicatively coupled to the commanddispatcher 318. The controller 310 can include a number of channels,e.g., 1, . . . , N, corresponding to the number of memory devices, e.g.,312-1, . . . , 312-N. The relationship between the number of channelsand the number of memory devices is described herein, and shown in thefigures, as being a one-to-one relationship; however, embodiments of thepresent disclosure are not so limited, and other configurations arecontemplated (e.g., multiple memory devices corresponding to aparticular channel, a particular memory device corresponding to multiplechannels, or combinations thereof). The front end DMA 316 and commanddispatcher 318 effectively communicatively couple the front end 344circuitry to the back end circuitry 346, e.g., back end channel 1(350-1), . . . , back end channel N (350-N). According to one or moreembodiments of the present disclosure, the controller 310 includes eightchannels, e.g., 1, . . . , 8. Embodiments of the present invention arenot limited to controllers having eight channels, thus, controllers maybe implemented having a greater or lesser quantity of channels thaneight.

Referring now to the back end portion 346 of controller 310, the backend portion 346 includes the number of channels, e.g., 350-1, . . . ,350-N. Each back end channel can include a channel processor, e.g.,356-1, . . . , 356-N, and associated channel DMA, e.g., 354-1, . . . ,354-N, each of which can be communicatively coupled to the front end DMA316. The command dispatcher 318 can be configured to distribute commandsto a respective channel processor, e.g., 356-1, . . . , 356-N, through achannel command queue, e.g., 355-1, . . . , 355-N. In one or moreembodiments, the channel command queues, e.g., 355-1, . . . , 355-N, canhold a number of commands received from the command dispatcher 318.

The front end DMA 316 can be configured to distribute data associatedwith a particular command to a corresponding channel DMA, e.g., 354-1, .. . , 354-N. The channel DMA, e.g., 354-1, . . . , 354-N, can becommunicatively coupled to a channel buffer, e.g., 358-1, . . . , 358-N,which in turn can be communicatively coupled to an error correcting code(ECC) and memory interface module, e.g., 360-1, . . . , 360-N. Thechannel processor, e.g., 356-1, . . . , 356-N, can also becommunicatively coupled to the ECC/memory interface, e.g., 360-1, . . ., 360-N, channel DMA, e.g., 354-1, . . . , 354-N, and channel buffer,e.g., 358-1, . . . , 358-N.

Although the embodiment shown in FIG. 3 illustrates each back endchannel 350-1, . . . , 350-N as including a back end channel processor,e.g., 356-1, . . . , 356-N, embodiments of the present disclosure arenot so limited. For example, the back end portion 346 can includecircuitry such as a shared back end processor, including, e.g., hardwarelogic such as an application-specific integrated circuit (ASIC), whichcan operate on a number of back end channels, e.g., 350-1, . . . ,350-N. Accordingly, the shared back end processor can be communicativelycoupled to communicate with the command dispatcher 318 and front end DMA316 analogous to that described for the dedicated channel processors,e.g., 356-1, . . . , 356-N. As shown in FIG. 3, a particular memorydevice, e.g., 312-1, . . . , 312-N, corresponds to each channel, e.g.,350-1, . . . , 350-N, such that the access to the particular memorydevice can be through the corresponding channel.

Host interface 314 can be the communication interface between thecontroller 310 and a host. In one or more embodiments, informationcommunicated between the host and the controller can include a number ofcommands, such as program (e.g., write) commands, read commands, erasecommands. The commands can be used to operate the associated memorydevice.

Command dispatcher 318 can receive a number of commands from the host,e.g., 202 in FIG. 2, through the host interface 314 and applicationlayer 320. Command dispatcher 318 can hold the received commands, andcan distribute commands to the respective channel command queue, e.g.,355-1, . . . , 355-N, of a number of respective back end channels, e.g.,350-1, . . . , 350-N, and to the front end DMA 316.

A payload can be associated with the command. For example, for a commandto write to memory, the associated payload can be the data that is to bewritten. The payload associated with a particular command can bereceived at the front end DMA 316 through the host FIFO 322 and AES 324.The front end DMA 316 can distribute data associated with a particularcommand in the command dispatcher 318 to a channel DMA, e.g., 354-1, . .. , 354-N, or directly to the corresponding channel buffer, e.g., 358-1,. . . , 358-N. The channel DMA, e.g., 354-1, . . . , 354-N, candistribute data associated with a particular command to thecorresponding channel buffer, e.g., 358-1, . . . , 358-N. In one or moreembodiments, the channel buffers, e.g., 358-1, . . . , 358-N, can holddata corresponding to a number of commands, the data being received fromthe front end DMA 316, through the channel DMA, e.g., 354-1, . . . ,354-N.

In one or more embodiments, the information communicated from the host,e.g., 202 in FIG. 2, to the command dispatcher 318 of the controller318, can include a number of commands, such as program commands, readcommands, and erase commands, among others. A program command can beused to write data to memory, e.g., memory devices 312-1, . . . , 312-N,a read command can be used to read data from memory, and an erasecommand may be used to erase a portion of the memory. The commands canindicate the type of operation, e.g., program, read, erase, along withthe start location, e.g., an LBA, and quantity, e.g., number of logicalsectors, of memory involved in the memory operation.

In one or more embodiments, an LBA can be associated with a logicalsector of the host, e.g., each logical sector of a host can beassociated with a particular LBA. For example, LBA 1000 can beassociated with a first logical sector, LBA 1001 can be associated witha second logical sector, LBA 1002 can be associated with a third logicalsector, etc. As a further example, a command to program the memory cellsin the array corresponding to 16 logical sectors of data starting at LBA1000 can program the memory cells associated with LBAs 1000 through1015, e.g., the memory cells corresponding to the logical sectors ofdata associated with LBAs 1000 through 1015. Thus, each logical sectorof data in a memory array can be referenced by a particular LBA. An LBAcan be mapped by the back end 346 to a physical address associated witha particular block of memory, e.g., a starting address of a particularblock of memory, or an LBA can mapped to a physical address associatedwith a particular sector within a block of memory, e.g., a startingaddress of a particular sector of memory.

FIG. 4 illustrates a logical-to-physical address map, implemented inaccordance with one or more embodiments of the present disclosure.Address map 461 illustrates the correlation between an LBA and aphysical block address (PBA) of the memory devices, e.g., 312-1, . . . ,312-N. For example, LBA 1 (462-1) corresponds to PBA A (464-1), LBA 2(462-2) corresponds to PBA B (464-2), LBA 3 (462-3) corresponds to PBA C(464-3), LBA 4 (462-4) corresponds to PBA D (464-4), . . . , and LBA M(462-M) corresponds to PBA M (464-M).

Receiving Commands

According to one or more embodiments of the present disclosure, thefront end DMA, e.g., 316 in FIG. 3, can include a command queue 386. Thefront end DMA, e.g., 316 in FIG. 3, can hold a number of commandsreceived from the host through the application layer 320 and commanddispatcher 318. Command dispatcher 318 can process the commands, anddistribute commands to the front end DMA 316 and a number of appropriateback end channels, e.g., 350-1, . . . , 350-N in FIG. 3. Operationsperformed by the command dispatcher, e.g., 318 in FIG. 3, can beimplemented in hardware, software, or a combination thereof. The commanddispatcher, e.g., 318 in FIG. 3, can include a command processor portionand a dispatcher portion. The command processor portion and a dispatcherportion may be discrete hardware modules, or the respective functionsmay be implemented in an integrated fashion by control circuitry.

Upon receiving a command from the host (hereinafter a “host command”),the command processor portion of the command dispatcher, e.g., 318 inFIG. 3, can check the integrity of the host command, and then pass thehost command along to the dispatcher portion of the command dispatcher.According to one or more embodiments of the present disclosure, thecommand processor portion of the command dispatcher, e.g., 318 in FIG.3, can be configured to check commands for acceptable LBA range and fora valid tag, among other integrity testing.

The dispatcher portion can distribute the host command to the front endDMA 316 and a number of appropriate back end channels, e.g., 350-1, . .. , 350-N in FIG. 3, and indicate to the application layer 320 thecompletion status of the command, e.g., whether it has been accepted andprocessed, which can be communicated to the host to indicate a next hostcommand may be sent. Implementing the functionality of the commanddispatcher in hardware can reduce host command processing time, e.g.,the time after receipt of a host command from the host to process thecommand and communicate (e.g., transmit or send) an indicator of thecommand completion status. Memory system throughput can be increased byreducing the processing time between host commands communicated betweenthe host and the memory system.

FIG. 5 is a block diagram of a command queue of a front end DMA, inaccordance with one or more embodiments of the present disclosure.Command queue 586 has a capacity of holding a quantity of C commands,e.g., the command queue can have a number of command slots, each commandslot able to hold a command, As shown in FIG. 5, command queue 586includes a number of command slots, e.g., command slot 1 (587-1),command slot 2 (587-2), . . . , command slot C (587-C). For example, inone or more embodiments, a front end DMA, e.g., 316 in FIG. 3, caninclude a number of command queues 386 having a capacity to store 32commands; however, embodiments of the present disclosure are not limitedto a particular number of commands slots, command queue capacity, ornumber of commands that can be processed simultaneously by the commanddispatcher.

In one or more embodiments, a front end DMA, e.g., 316 in FIG. 3, canreceive host commands from the host in an initial order. The number ofcommand queues 386 can hold the number of host commands in the initialorder, e.g., in the order they are received from the host. The commandqueues 386 can hold a finite number of commands at one time; therefore,the command dispatcher is configured to signal the host when the commandqueue 386 has reached its capacity, and is temporarily unable to receivefurther host commands from the host.

In one or more embodiments, the command dispatcher, e.g., 318 in FIG. 3,can process the host command held in the task file 315 and candistribute it to the command queue 386 in the front end DMA 316. Thecommand dispatcher 318 can then distribute the host commands from thecommand queue 386 to the back end channels in an order in which theywere received and are queued in the command queue 386, e.g., in an orderin which host commands are to be executed, in an order in which hostcommands can be distributed, in a combination of the aforementionedorders, or according to some other appropriate ordering scheme.

In one or more embodiments, the command processor portion of the commanddispatcher is configured to determine whether the commands held in thecommand queue(s) 386 can be modified, e.g., to optimize distribution ofthe number of commands among the plurality of back end channels, and tomodify host commands, individually or as a group. Modifying commands toeconomize distribution can include, for example, combining commands toadjacent memory locations and/or deleting commands that are subsequentlyoverwritten without being read from, so that fewer commands are sent toaccomplish the same net change to the memory for writing operations orto accomplish the same net read from memory for reading operations,thereby saving time, processing resources, and/or communicationbandwidth, among others. As used herein, commands can include hostcommands, host commands that have been modified, and other types ofcommands. The command processor portion can analyze and modify commandsin the command queue 386 in order to more efficiently distributecommands to the respective channels, make individual commands moreefficient, improve reliability of the memory system, improve performanceof the memory system, reduce wear of the memory system, or improve thequality, efficiency, or flow of commands among the respective back endchannels. For example, the command processor portion can re-ordercommands within a group of commands, combine (e.g., coalesce) commandsby grouping multiple commands into one or more commands, or determinethat a particular command is not to be executed (e.g., when it can bedetermined that a subsequent command will modify data at a particularmemory location), among other command optimization techniques. In one ormore embodiments, the front end processor (FEP) 328 can also performthese tasks and make these determinations.

FIGS. 6A and 6B illustrate operation of a command queue of a front endDMA, in accordance with one or more embodiments of the presentdisclosure. According to one or more embodiments, the commanddispatcher, e.g., 318 in FIG. 3, and/or FEP, e.g., 328 in FIG. 3, candetermine whether the commands held in the command queue of a front endDMA, e.g., 386 in FIG. 3, can be modified, and the command dispatchercan be configured to modify the commands in a manner intended toexpedite command throughput of the front end of the controller, e.g.,344 n FIG. 3.

In order to increase command throughput, in one or more embodiments, thecommand dispatcher 318 or FEP 328 processes host commands to increasethroughput only when back end channels are busy (e.g., when associatedchannel buffers are full). When the back end channels are busy, such aswhen the associated channel buffers (e.g., 358-1, . . . , 358-Nrespectively) are full, the front end portion of the controller may beprevented from distributing commands to the back end channels. To theextent that a number of the back end channels are able and willing toaccept additional commands, commands should not be delayed to accomplishfurther optimization processing by the command dispatcher, becausedelaying emptying the command queue 686A/B delays completion of hostcommands in the command queue 686A/B, which in turn delays transfer ofadditional commands from the host, and further optimization of commandsmay take place in respective channel command queue (perhaps with evengreater efficiency) without causing delay in distributing commands toother back end channels. Additional detail on the operation of back endchannels can be found in commonly assigned U.S. patent application Ser.No. 12/351,206, entitled “Modifying Commands”, having at least onecommon inventor, and having attorney docket number 1002.0430001.

In one or more embodiments, command queue 686A can be analogous tocommand queue 386 discussed with respect to FIG. 3. Command queue 686Aincludes a number, e.g., C, of command slots, e.g., 687-1A, 687-2A,687-3A, 687-4A, 687-5A, 687-6A, 687-7A, 687-8A, . . . , 687-CA. Each ofthe C command slots can be configured to temporarily store a command,e.g., a host command. For example, command slot 687-1A can store a firstcommand, command slot 687-2A can store a second command, and so on.

In an example discussed below with respect to a front end commanddispatcher processing commands in the command queue 686A, andillustrated in FIG. 6A, the command in command slot 1, e.g., 687-1A, canbe a command to program, e.g., write, data to memory cells in a memorydevice involving 16 logical sectors starting at LBA 1000. The command incommand slot 2 e.g., 687-2A, can be a command to read data from memorycells in the memory device involving 4 logical sectors starting at LBA2000. The command in command slot 3 e.g., 687-3A, can be a command toprogram data into the memory cells in the memory device involving 48logical sectors of data starting at LBA 1000. The command in commandslot 4, e.g., 687-4A, can be a command to read the data in the memorycells in a memory device involving 10 logical sectors of data startingat LBA 2002. The command in command slot 5, e.g., 687-5A, can be acommand to read memory cells in the memory device involving 16 logicalsectors of data starting at LBA 2000. The command in command slot 6,e.g., 687-6A, can be a command to program memory cells in the memorydevice involving 16 logical sectors of data starting at LBA 1040. Thecommand in command slot 7, e.g., 687-7A, can be a command to programmemory cells in the memory device involving 2 logical sectors of datastarting at LBA 3000. The command in command slot 8, e.g., 687-8A, canbe a command to program memory cells in the memory device involving 2logical sectors of data starting at LBA 3002.

The commands held in the command queue 686A at any particular time maybe associated with one memory device, e.g., all corresponding to thesame channel, or may be associated with a number of different memorydevices, e.g., corresponding to a plurality of channels. The particularchannel with which a command is associated can be determined from theLBA, according to the amount and division of physical memory withrespect to each channel, as mapped by a logical-to-physical address map,e.g., address map 461 in FIG. 4. For example, the physical block addressmay include channel identification information.

The commands held in command queue 686A can be modified in accordancewith one or more embodiments of the present disclosure. For example, thecommands in command slots 687-1, 687-3, and 687-6 may be combined into asingle command to program the memory cells involving 56 logical sectorsstarting at LBA 1000. Thus, the command dispatcher can be configured todetermine that at least two commands are for a same operation, e.g., awrite operation but involving logically adjacent memory locations. Thecommand dispatcher can optimize distribution of commands to the back endchannels by combining the at least two commands into a single commandinvolving the combination of the logically adjacent memory locations.The combined command is most efficient where the logically adjacentmemory locations are associated with a single channel.

FIG. 6B illustrates a block diagram of channel command queue 686B afterthe commands shown in FIG. 6A have been modified in accordance with oneor more embodiments of the present disclosure. As shown in FIG. 6B,command 1 held in channel command slot 687-1B is a command to programthe memory cells in the array corresponding to 56 logical sectors of thehost starting at LBA 1000. Command 2 held in channel command slot 687-2Bis a command to read the memory cells in the array corresponding to 16logical sectors of the host starting at LBA 2000, and command 3 held inchannel command slot 687-3B is a command to program the memory cells inthe array corresponding to 4 logical sectors of the host starting at LBA3000.

The command dispatcher can also be configured to determine that at leasttwo commands are for a same operation, e.g., a write operation butinvolving logically overlapping memory locations, e.g., the memorylocation involved with one command includes at least a portion of amemory location involved with another command of the same type. Thecommand dispatcher can optimize distribution of commands to the back endchannels by combining the at least two commands into a single commandinvolving the combination of the logically overlapping memory locations.

Other command modifications may be possible. For example, where thecommand processor portion can determine that a first command in commandqueue 686A involving a particular memory location, e.g., LBA, may beexecuted before a second command which will overwrite the particularmemory location, the command processor portion may not distribute (e.g.,delete, ignore, not execute) the first command to its destinationchannel since the results thereof will only be temporary, e.g., untilthe second command is executed.

The above-mentioned example can be further understood with respect toFIG. 6. Assuming commands nearer the top of the command queue 686A,e.g., command slot 687-1, are to be executed before commands nearer thebottom of the command queue 686A, e.g., command slot 687-C. The LBA ofthe commands in command slot 1, e.g., 687-1A, and command slot 3 e.g.,687-3A, are both 1000. Command 1 and command 3 are both programoperations. Since command 3 will program 48 sectors starting at LBA1000, command 3 will completely overwrite whatever is programmed in the16 sectors starting with LBA 1000 as a result of command 1. There is anintervening read operation, e.g., command 2; however, command 2 does notinvolve the 16 sectors starting with LBA 1000. Therefore, command 1 neednot be distributed (e.g., deleted, ignored, not executed), therebysaving time by not having to transfer command 1 to a channel andoptimizing the distribution of commands from the command queue 686A andamong the plurality of back end channels, as well as the speed at whichthe command queue 686A may accept additional host commands. Othercommand re-ordering, combining, and deleting may be possible tooptimize, e.g., economize, distribution of the commands shown in commandqueue 686A to the number of back end channels.

The command dispatcher thus can be configured to determine a net changeto memory to be accomplished by the number of commands in the commandqueue 686A, and modify the number of commands held in the command queue686A based on the determination, thereby optimizing distribution of thenumber of commands among the plurality of back end channels. The commanddispatcher can be configured to not distribute (e.g., delete, ignore,not execute) one of the number of commands from the command queue 686Awhen the command dispatcher can determine from the commands held in thecommand queue 686A at any given time that doing so will not change thedetermined net change to memory by the number of commands. For example,the command dispatcher can be configured to modify a memory rangeassociated with a first command in the command queue 686A to include aportion of the memory range of a second command in the command queue686A, and thereafter delete the second command from the command queue686A without changing the determined net change to memory to beaccomplished by the number of commands.

As described above, the dispatcher portion of the command dispatcher candistribute commands, e.g., host commands, to a number of appropriatechannels. The dispatcher portion can distribute a particular command toan appropriate channel, for example, where a payload associated with theparticular command involves a single channel. For a payload involvingmultiple channels, the dispatcher portion can manage the distribution ofthe associated command by distributing the particular command to themultiple channels, including its channel-specific parameters foroperating the respective memory devices corresponding to the particularlogical block address and sector count associated with a command. Thepayload associated with the command can then be parsed, with potionsthereof being distributed among the multiple channels, e.g., in a roundrobin fashion. Similarly for a read operation, the payload associatedwith a read command may be distributed among multiple backend channels,and a corresponding read command may be distributed to the associatedbackend channels in order to assemble data from among the multiplechannels.

Each back end channel can, for example, process R consecutive logicalblock addresses (LBAs), but a host command (i.e., a command receivedfrom a host) can involve a relatively large number of sectors. Thecommand dispatcher can distribute back end commands in a round robinfashion among a number of back end channels, where each back end commandmimics the host command except that each back end command involves Rconsecutive LBAs. The round robin process continues until all of thesectors of the host command are distributed in R-size “chunks” among theback end channels.

For further illustration, consider the following numerical example,where a host command is to write 128 sectors of data, where there are 4back end channels, and where each back end channel can process 8consecutive LBAs. For simplicity, memory location offsets will beignored in this example. Upon receipt of the host write commandinvolving 128 sectors, multiple back end write commands are generated inresponse to the single host write command. A first back end writecommand can involve a first 8 LBAs going to back end channel 1, then asecond back end write command can involve the next 8 LBAs going to backend channel 2, a third back end write command can involve the next 8LBAs going to back end channel 3, a forth back end write command caninvolve the next 8 LBAs going to back end channel 4. This round robinprocessing continues with the first back end write command alsoinvolving the next 8 LBAs going to back end channel 1, until all 128sectors are distributed among the 4 channels.

As a result, each channel will have received 32 sectors of payloadcorresponding to the host write command, but assembled as a collectionof 8 LBA portions strung together. Thereafter, the respective writecommand is distributed to the respective back end channels to write 32sectors of data. Thus, a single host command can result in N back endcommands (where there are N back end channels), each mimicking the hostcommand action but involving approximately 1/Nth of the payloadassociated with the host command. Only one command per channel isdistributed, along with a respective portion of the payload associatedwith the host command. Embodiments of the present disclosure are notlimited to the numerical example quantities described here, and are notlimited to write commands. One skilled in the art will understand thatother commands (e.g., read commands) may be similarly distributed inparallel among multiple channels (e.g., to read data from among a numberof back end channels) resulting from a single host command.

In one or more embodiments, commands in the command queue 686A can bemodified by combining a number of commands into a single command so asto eliminate or reduce partial page programming operations, e.g.,combining partial pages together into a single operation. In addition toimproving performance and reliability of the memory system by reducingwear associated with partial page programming, combining commands in thefront end command queue 686A optimizes distribution of the number ofcommands among the plurality of back end channels, since multipleprogramming commands can be reduced to a fewer number of commands, e.g.,a single command.

Partial page programming operations are performed by finding a new blockof memory cells that is free, reading a page from an old block into adata buffer, merging new data in to the data buffer, writing the entirepage (including the merged data) to a new page of memory in a new block,moving all the other pages of the old block to a new block, and markingthe old block to indicate that it is to be erased. While severalexamples have been given to illustrate algorithms used for combiningcommands which optimizes distribution of the number of commands amongthe plurality of back end channels, embodiments of the presentdisclosure are not limited to the examples provided, and the presentdisclosure contemplates other optimizing techniques, such as those thatinvolve deleting or re-ordering commands at the front end to reduce thequantity of commands that are distributed among the plurality of backend channels.

In one or more embodiments, a memory controller includes a plurality ofback end channels, and a command queue, e.g., 386 in FIG. 3,communicatively coupled to the plurality of back end channels. Thecommand queue, e.g., 386 in FIG. 3, can be configured to hold hostcommands received from a host. Circuitry is configured to generate anumber of back end commands at least in response to a number of the hostcommands in the command queue, e.g., 386 in FIG. 3, and distribute thenumber of back end commands to a number of the plurality of back endchannels.

The number of back end commands can be fewer, or greater, than thenumber of the host commands. For example, in one or more embodiments thecircuitry can be configured to generate a back end command correspondingto each of the plurality of back end channels in response to a singlehost command. The circuitry can be further configured to distribute thecorresponding back end command to its respective back end channel suchthat the back end commands are processed substantially in parallel. Inone or more embodiments the circuitry can be configured to distributemultiple host commands among different multiple back end channels suchthat the multiple host commands are executed substantiallysimultaneously.

Generating the number of back end commands can include the combinationof modifying at least one of the number of host commands and deleting atleast another one of the number of host commands. A Direct Memory Accessmodule (DMA) can be configured to distribute data associated with a hostcommand corresponding to the number of back end commands generated.

Upon completion of a respective back end command, the circuitry can beconfigured to communicate to the host results from executing aparticular one of the multiple back end commands upon completion of theparticular one of the multiple back end commands, without regard tocompletion of execution of any other of the multiple back end commands.

FIG. 7 is a flow diagram for distributing commands among a number ofback end channels, in accordance with one or more embodiments of thepresent disclosure. The command distribution starts at 766. At 767 thestarting LBA of a distributed command can be set to the sum of a commandLBA and an LBA offset. The starting channel can be determined, e.g.,calculated, along with the starting channel sector count, endingchannel, ending channel sector count, remaining sector count and achannel starting LBA. At 768 the channel number, e.g., to which thecommand is initially distributed, can be set to the starting channel.Then at 769, a starting LBA and sector count can be determined, e.g.,calculated, for the current channel, and the channel involved statusbit, e.g., involved_ch, can be asserted for the particular currentchannel number to indicate that a particular channel is involved with aparticular command.

Next at 770, the starting LBA and sector count for the current channelare loaded to the current channel's inbox (channel inboxes are discussedfurther below). Whether the current channel is the end channel (see 767)can be determined at 771. If the current channel is not the end channel,the distribution process moves to the next channel, e.g., the currentchannel number can be incremented, at 773, and the process continues at769 (the starting LBA and sector count for the current channel areloaded to the current channel's inbox). If the current channel is theend channel, the start channel, channel sector count and channelsinvolved are loaded to the DMA Descriptor Block (DDB; discussed furtherbelow) at 772, and the process returns to start the next commanddistribution back at 766.

FIG. 8 is a functional block diagram illustrating one embodiment of aninterface between a front end and a number of channels, in accordancewith one or more embodiments of the present disclosure. FIG. 8 shows anumber of channels, e.g., 850-1, . . . , 850-N, located in a back endportion 846 of a memory controller, which may be analogous to channels350-1, . . . , 350-N shown in FIG. 3; however, some of the channeldetail shown on FIG. 3 is omitted for clarity in FIG. 8 so thatadditional structure may be shown in greater detail. FIG. 8 also shows afront end DMA 816 and front end processor 828 (FEP) located in a frontend portion 844 of the memory controller. The front end DMA 816 may beanalogous to the front end DMA 316 in FIG. 3, and the FEP 828 may beanalogous to the FEP 328 in FIG. 3. The front end DMA 816 and the FEP828 are respectively shown in FIG. 8 as being communicatively coupled toeach of the number of channels, e.g., 850-1, . . . , 850-N, in a mannerdescribed in further detail below.

Each channel includes a channel processor, e.g., 856-1, . . . , 856-N, achannel in-box, e.g., 874-1, . . . , 874-N, a channel in-register, e.g.,876-1, . . . , 876-N, and a channel out-register, e.g., 878-1, . . . ,878-N. Each of the channel out-register and in-box are communicativelycoupled to provide information to the FEP 828. Each of the channelin-box and in-register are communicatively coupled to receiveinformation from the front end DMA 816.

Front End Direct Memory Access (DMA)

FIG. 9A is a functional block diagram of a Direct Memory Access module(DMA) Descriptor Block, implemented in accordance with one or moreembodiments of the present disclosure. A DDB controls data flow betweenthe host and the back end channels, and functions to optimize systemthroughput, e.g., using intelligent decision making relative to commandsheld in the command queue, e.g., 386 in FIG. 3, in order to increase theefficiency of distributing the commands from the command queue, e.g.,386 in FIG. 3, to the various back end channels and thereby increasingthe speed of commands thorough the command queue, e.g., 386 in FIG. 3.

For a memory system having a number of memory devices accessed throughcorresponding channels, e.g., a solid state drive, the payloadassociated with a write command can be programmed to a number ofchannels, and the payload associated with a read command may beassembled from a number of channels. In managing a payload associatedwith a particular command that involves multiple channels, the DMAdistributes the data among the appropriate channel(s). For example, theDMA manages distributing a payload associated with a write command to anumber of channels, and assembling a payload associated with a readcommand from a number of channels. The DMA also facilitates multiple,including parallel, command execution by managing the payload associatedwith multiple commands between the host and back end channels.

The DDB, e.g., 340 in FIG. 3, coordinates the distribution of payload toand from the N channels when a command is issued. For example, during awrite or read operation, a number of the N channels can be used. The DDBcan be first updated, e.g., loaded, by the command dispatcher, e.g., 318in FIG. 3, or the front end processor (FEP), e.g., 328 in FIG. 3, wherethe DDB TAG can be the address for each host command. The DDB can be setup by either the FEP or the command dispatcher. No further management bythe FEP of the I/O processor can be necessary during “no error”conditions.

FIG. 9A shows the contents of a DDB 988 having a number of TAG addressentries, e.g., DDB 1, . . . , DDB 32. Each TAG address entry containsparameters associated with the set up 990, the status 992, and commandinformation 994 associated with a data transfer. According to one ormore embodiments of the present disclosure, the TAG addressing may beimplemented according to Serial Advanced Technology Attachment (SATA)standards. Thus the DDB entry can determine which channel to access, howmany sectors to transfer for a particular channel, and the associatedstatus, among other information. DDB can be backwards compatible byusing only DDB 1 for legacy commands that do not support multiplecommand queuing, e.g., only one legacy command is processed through theDDB at a time instead of multiple commands being simultaneously managedin the DDB.

Each entry in the DDB 988 has a TAG, which can be either assigned orimplied. In one or more embodiments, the TAG can be the same as theentry number, e.g., the physical position of the entry in the DDB, thus,the physical location of the entry in the DDB implies the TAG so that anactual TAG number field need not be stored with each entry. As thecontroller receives a host command, and it adds a new entry to the DDBcorresponding to the host command, each entry being associated with aTAG, and outputs the TAG associated with the new entry. The controllermaintains a command queue, e.g., 386 in FIG. 3, as previously described,receives the TAG associated with the new entry, adds a new command queueentry corresponding to the TAG, and outputs a range operation request.

FIG. 9B illustrates an entry in the DMA Descriptor Block (DDB)illustrated in FIG. 9A, implemented in accordance with one or moreembodiments of the present disclosure. FIG. 9B indicates data fields ofa DDB entry by type, (e.g., set-up, status, info), description, size(e.g., number of bits), and location within the entry (e.g., bitpositions).

The next count data field 990A of each DDB entry, e.g., “next_cnt” atbit positions 93-96, represents the number of sectors of data totransfer for one given channel. The next count can be initialized by thecommand dispatcher or FEP to specify the first transfer count of thestarting channel. The next count can be updated by hardware to specifythe transfer count of the preceding channel. The update occurs after thecurrent channel completes its transfer, but before the overall transferis complete. If the remaining number of overall sectors to transfer isgreater than the maximum amount of sectors a channel can transfer, e.g.,the count is greater than the sector count per page times the number ofplanes, then next count can be loaded with that maximum amount ofsectors. Otherwise, next count can be loaded with the remaining numberof overall sectors to transfer.

The count data field 990B, e.g., “cnt” at bit positions 80-95, can bethe overall transfer count for a particular command. The count can beinitialized by the command dispatcher or FEP with the total transfercount and can be updated by hardware to indicate the remaining number ofsectors to transfer. According to one or more embodiments, bit position79 is not used, e.g., it is reserved for future use.

The transfer complete data field 990D, e.g., “XC” bit at position 78,indicates that the DMA transfer is complete. That is, the data phase maybe completed, but the indicator of command complete status may not havebeen sent. This bit can be set by hardware once channel status(“ch_status”) is equal to a particular value, to indicate that the hostcommand is complete. Hardware then schedules the sending of theindicator o a command complete status. When the indicator issuccessfully sent to the host, the hardware operates to clear the validdata field, e.g., “V” flag, before another host command can be received,as described later.

The host error data field 992A, e.g., “HE” bit at position 77, can beused to indicate that an error occurred. This bit can be set by the I/Oprocessor or the host interface, e.g., 314 in FIG. 3, if the erroroccurs during host transfer. The flash error data field 992B, e.g., “FE”bit at position 76, can be used to indicate that a memory device, e.g.,NAND flash, error occurred.

The valid data field 992C, e.g., “V” bit at position 75, can be used toindicate a valid entry. This bit can be set by the command dispatcher orFEP, e.g., V=1, to indicate that the hardware has access to the DDBentry, and the command dispatcher or FEP may not over-write the entry.This bit can be cleared by hardware after host command is completed andthe indicator has been successfully sent to the host, or it can becleared by FEP when there is an error while processing the command,e.g., V=0, to indicate that entry in the DDB is available to receive anew command from host.

The next channel data field 992D, e.g., “nxt_ch” at bit positions 72-74,refers to the channel where the transfer will occur. This field can beinitialized by the command dispatcher or FEP to specify the startingchannel for the transfer and can be updated by hardware to specify thenext channel for transfer. Updates occur when the previous channelfinishes transferring all of the consecutive LBAs that the channel canprocess. The sector count for the particular command may not havereached zero, since there may be remaining sectors to transfer for theparticular command, including additional rounds to the channel as partof a round-robin distribution, as described above. For one channel, thesector count for the particular command will reach zero, when there areno remaining sectors to transfer for the particular command, e.g., thelast channel in a round robin sequence to which payload is distributed.

The active channel data field 992E, e.g., “active_ch” at bit positions64-71, can be an N-bit signal, e.g., 8-bit corresponding to 8 channels,where each bit represents the completion status of its respectivechannel. Before a transfer occurs, the bits corresponding to eachinvolved channel can be set. Each bit can then be reset once the commandis complete for that channel.

The command information data field 994, e.g., “CMD_info” at bitpositions 0-63, can comprise four words from a Frame InformationStructure (FIS) register, including command, priority bit, FUA bit, LBA,and sector count.

Although particular data field sizes, e.g., one bit, and data fieldpositions are described in the example above, embodiments of the presentdisclosure are not limited to those including every such describedfield, or to the specific data field sizes or positions, and may includeadditional or alternative fields. When the command dispatcher isupdating the DDB, an input signal, e.g., “xfer_TAG,” becomes the DDB'saddress pointer and an update signal, e.g., “update_ddb_en,” becomes thewrite enable.

The arbiter, e.g., 342 in FIG. 3, can be a round robin arbiter thatdetermines which channel can be accessed at a particular time. Thearbiter searches for the next available channel. The arbiter stepsthrough the channels, attempting to match a selected available channelnumber with the next channel in a particular DDB entry. If the availablechannel does not match the DDB entry, the arbiter continues, repeatingin round robin fashion if necessary, until a match between a selectedavailable channel number and the next channel in a particular DDB entrycan be found. Once a match is found, the arbiter initiates acommunication protocol to start the transfer. At the completion of atransfer, a completion protocol can be signaled, channel information inthe DDB entries are updated, and the arbiter searches for the nextavailable channel.

Each of the N bits of the active channel field 992E, e.g., register, ofa particular TAG entry corresponds to a respective one of the Nchannels. Once a channel can be deemed available for a particular hostcommand, the bit associated with that channel can be set. When a channelcompletes transfers to the particular channel for a given host command,the channel's command complete status can be set, which in turn, canreset the respective bit in the active channel field of the DDB entry.Once all bits of the active channel are reset, an indicator of the“complete” status of a host command can be issued to the applicationlayer. The application layer can then send an indicator of the“complete” status of the host command to the host. The valid bit of theentry can be cleared (e.g., V=0) by hardware after the host command iscompleted and an indicator of the “complete” status has beensuccessfully sent to the host, or it can be cleared by a FEP, forexample, when there is an error while processing the command to indicatethat the entry in the DDB is available to receive a new command from thehost.

Command completions are based on a back end channel indicating that arequested transfer is complete. According to one or more embodiments ofthe present disclosure, during read operations associated with multiplecommands being executed simultaneously across multiple channels, the DMAtransmits data from any of the channels to the host as soon as the datais ready regardless of the order in which the commands were receivedfrom the host. Memory system data throughput can be substantiallyincreased by executing commands, e.g., transferring data read from thememory devices back to the host, in the order in which the commands havebeen at least partially completed by each back end channel, rather thanin the order in which the commands were received or initiated.

For example, a first read command can be received by the memory systemfrom the host and execution by the memory system can be initiated,followed by a second read command being received by the memory systemfrom the host and its execution by the memory system being initiated.However, the second read command can be completed first. According toone or more embodiments, rather than wait for completion of the firstread command so that its data can be returned first to the host, thedata resulting from the second read command can be returned to the hostbefore the data resulting from the first read command can be returned tothe host.

For another example, a first read command can be received by the memorysystem from the host, followed by a second read command being receivedby the memory system from the host. However, for efficiency, the memorysystem can re-order the commands, e.g., in a manner previouslydescribed, and execute the second read command before executing thefirst read command, which results in the second read command beingcompleted before the first read command. According to one or moreembodiments, rather than wait for completion of the first read command,the data resulting from the second read command can be returned to thehost as it is completed, which can be before the data resulting from thefirst read command can be returned to the host.

In operating multiple memory devices, the payload associated with asingle command, portions of which have a certain sequential orderrelating them to one another, can be distributed across differentchannels, e.g., a first portion of the payload may be stored in a firstmemory device and a second portion of the payload may be stored in asecond memory device, etc. Therefore, portions of the data, e.g.,resulting form a read command, may be returned to the front end of thecontroller from the different memory devices (and associated channels)out of sequential order, e.g., the second portion may be retrieved fromthe second memory device before the first portion can be retrieved fromthe first memory device. According to one or more embodiments, when DMAbuffer offset can be supported, the portions can be transferred back tothe host out of sequential order, in the order the commands arecompleted by the respective back end channels, rather than in thesequential order in which the portions are related.

In other words, a number of portions of a payload associated with asingle command are stored, e.g., reside, among several memory devices ofa solid state drive. The portions of the payload are related to oneanother by a particular order in forming the payload. A single readcommand can be used to assemble the payload from among several memorydevices, the read command being appropriately customized with respect toparticular memory location and distributed to each of the severalchannels corresponding to the several memory devices in order to receivea respective portion of the payload from each of the several memorydevices. According to one or more embodiments, the portions are receivedby the memory system controller and sent to the host as they arereceived, in an order that can be different than the particular orderthat the portions of the payload are related to one another in formingthe payload. In other words, the portions of the payload are notreassembled into the payload before being sent to the host, and insteadportions of the payload are sent as they are received to the controllerfrom among the several memory devices.

According to one or more embodiments of the present disclosure, duringoperations of multiple commands, e.g., write commands, being executedsimultaneously across multiple channels, e.g., to corresponding multiplememory devices, the DMA can send an indicator of the command completionstatus for a particular command to the host upon completion of thecommand, which allows the host to send the next pending command. In oneor more embodiments, the multiple channels are asynchronous channels,and command, e.g., host command, execution may not occur in the sameorder as the command was received from the host (relative to othercommands received from the host).

For example, a first command can be received by the memory system fromthe host and its execution initiated by the memory system, followed by asecond command being received by the memory system from the host and itsexecution initiated by the memory system. However, the second readcommand can be completed first by a number of the multiple back endchannels. According to one or more embodiments, rather than wait forcompletion of the first command so that an indicator of the completionstatus of the first command can be sent to the host before an indicatorof the completion status of the second command can be sent to the host,the indicator of the completion status of the second command can be sentto the host before the indicator of the completion status of the firstcommand is sent to the host.

For another example, a memory controller, e.g., of a memory system,receives a first command from the host, followed by receipt of a secondcommand by the memory controller from the host. However, the memorysystem re-orders the commands, e.g., in a manner previously described,and executes the second command before executing the first command,which results in the second command being completed before the firstcommand. According to one or more embodiments, rather than wait forcompletion of the first command so that an indicator of the completionstatus of the first command can be sent to the host before an indicatorof the completion status of the second command can be sent to the host,the indicator of the completion status of the second command can be sentto the host before the indicator of the completion status of the firstcommand is sent to the host.

CONCLUSION

The present disclosure includes memory controllers, memory systems,solid state drives and methods for processing a number of commands. Inone or more embodiments, a memory controller includes a plurality ofback end channels, and a command queue, e.g., 386 in FIG. 3,communicatively coupled to the plurality of back end channels. Thecommand queue 386 can be configured to hold host commands received froma host. Circuitry is configured to generate a number of back endcommands at least in response to a number of the host commands in thecommand queue 386, and distribute the number of back end commands to anumber of the plurality of back end channels.

The present disclosure also includes methods and devices for a memorycontroller. In one or more embodiments, a memory controller includes aplurality of back end channels, and a front end command dispatchercommunicatively coupled to the plurality of back end channels. Thecommand dispatcher is communicatively coupled to a command queue, e.g.,386 in FIG. 3, which is configured to buffer a number of commands. Thecommand dispatcher can be configured to determine a net change to memoryto be accomplished by the number of commands and modify at least one ofthe number of commands based on the determination to optimizedistribution of the number of commands among the plurality of back endchannels.

In the detailed description of the present disclosure, reference is madeto the accompanying drawings that form a part hereof, and in which isshown by way of illustration how one or more embodiments of the presentdisclosure may be practiced. These embodiments are described insufficient detail to enable those of ordinary skill in the art topractice the embodiments of this disclosure, and it is to be understoodthat other embodiments may be utilized and that process, electrical orstructural changes may be made without departing from the extent of thepresent disclosure.

As used herein, the designators “N,” “M,” and “C,” particularly withrespect to reference numerals in the drawings, indicate that a number ofthe particular feature so designated can be included with one or moreembodiments of the present disclosure. As will be appreciated, elementsshown in the various embodiments herein can be added, exchanged, oreliminated so as to provide a number of additional embodiments of thepresent disclosure. In addition, as will be appreciated, the proportionand the relative scale of the elements provided in the figures areintended to illustrate the embodiments of the present disclosure, andshould not be taken in a limiting sense.

It will be understood that when a first element is referred to as being“connected to” or “coupled with” another element, the element isphysically attached to the of the two elements is intended. In contrast,when elements are referred to as being “communicatively coupled,” theelements are in communication with one another, including but limitedto, by hardwired or wireless signals paths.

It will be understood that when an element is referred to as being “on,”“connected to” or “coupled with” another element, it can be directly on,connected, or coupled with the other element or layer or interveningelements or layers may be present. In contrast, when an element isreferred to as being “directly on,” “directly connected to” or “directlycoupled with” another element or layer, there are no interveningelements or layers present. As used herein, the term “and/or” includesany and all combinations of a number of the associated listed items.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions,layers, and sections, these elements, components, regions, wiring lines,layers, and sections should not be limited by these terms. These termsare only used to distinguish one element, component, region, wiringline, layer, or section from another region, layer, or section. Thus, afirst element, component, region, wiring line, layer or sectiondiscussed below could be termed a second element, component, region,wiring line, layer, or section without departing from the teachings ofthe present disclosure.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures rather than an absoluteorientation in space. It will be understood that the spatially relativeterms are intended to encompass different orientations of the device inuse or operation in addition to the orientation depicted in the figures.For example, if the device in the figures is turned over, elementsdescribed as “below” or “beneath” other elements or features would thenbe oriented “above” the other elements or features. Thus, the exampleterm “below” can encompass both an orientation of above and below. Thedevice may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used hereininterpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises” and“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, or components,but do not preclude the presence or addition of a number of otherfeatures, integers, steps, operations, elements, components, or groupsthereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and should not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Embodiments of the present disclosure are described herein withreference to functional block illustrations that are schematicillustrations of idealized embodiments of the present disclosure. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and tolerances, are to be expected.Thus, embodiments of the present disclosure should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing. For example, a region illustrated or described as flatmay, typically, have rough or nonlinear features. Moreover, sharp anglesthat are illustrated may be rounded. Thus, the regions illustrated inthe figures are schematic in nature and their shapes and relative sizes,thicknesses, and so forth, are not intended to illustrate the preciseshape/size/thickness of a region and are not intended to limit the scopeof the present disclosure.

Although specific embodiments have been illustrated and describedherein, those of ordinary skill in the art will appreciate that anarrangement calculated to achieve the same results can be substitutedfor the specific embodiments shown. This disclosure is intended to coveradaptations or variations of one or more embodiments of the presentdisclosure. It is to be understood that the above description has beenmade in an illustrative fashion, and not a restrictive one. Combinationof the above embodiments, and other embodiments not specificallydescribed herein will be apparent to those of skill in the art uponreviewing the above description. The scope of the one or moreembodiments of the present disclosure includes other applications inwhich the above structures and methods are used. Therefore, the scope ofone or more embodiments of the present disclosure should be determinedwith reference to the appended claims, along with the full range ofequivalents to which such claims are entitled

In the foregoing Detailed Description, some features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the disclosed embodiments of the presentdisclosure have to use more features than are expressly recited in eachclaim. Rather, as the following claims reflect, inventive subject matterlies in less than all features of a single disclosed embodiment. Thus,the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment.

1.-20. (canceled)
 21. A solid state drive, comprising: a plurality offlash memory devices; a memory controller, comprising: a plurality ofback end channels, each communicatively coupled to a number of theplurality of memory devices; a front end direct memory access (DMA)communicatively coupled to the plurality of back end channels; and afront end command dispatcher communicatively coupled to the DMA having acommand queue configured to hold a number of commands; wherein thecommand dispatcher is configured to process commands to modify theirdistribution among the plurality of back end channels based on thenumber of commands then held in the command queue.
 22. The solid statedrive of claim 21, wherein the front end DMA is configured to process arespective payload associated with at least one command that involvesmore than one of the plurality of back end channels.
 23. The solid statedrive of claim 21, including a Serial Advanced Technology Attachment(SATA) interface communicatively coupled to the memory controller, theSATA interface being configured to communicate with a host.
 24. Thesolid state drive of claim 21, wherein each of the plurality of back endchannels is communicatively coupled to a respective one of the pluralityof memory devices.
 25. The solid state drive of claim 24, wherein theplurality of flash memory devices comprises eight NAND flash memorydevices.
 26. The solid state device of claim 24, wherein the pluralityof back end channels comprises eight back end channels.
 27. The solidstate drive of claim 21, wherein the command dispatcher is configured toprocess commands on a front end of the controller to optimize theirdistribution to a back end of the controller by selectively reorderingcommands, selectively combining commands, and/or selectively deletingcommands.
 28. The solid state drive of claim 27, wherein each of theplurality of back end channels is configured to further processrespectively received commands to expedite the execution of therespectively received commands by selectively reordering receivedcommands, selectively combining received commands, and/or selectivelydeleting commands.
 29. A solid state drive, comprising: a plurality offlash memory devices; a memory controller, comprising: a plurality ofback end channels, each communicatively coupled to a number of theplurality of memory devices; a front end direct memory access (DMA)communicatively coupled to the plurality of back end channels; and afront end command dispatcher communicatively coupled to the DMA having acommand queue configured to hold a number of commands; wherein the frontend DMA is configured to: receive the number of commands in a particularorder; and process a respective payload associated with at least onecommand of the number of commands; and wherein the command dispatcher isconfigured to process the number of commands to optimize theirdistribution among the plurality of back end channels by modifying theparticular order of the number of commands.
 30. The solid state drive ofclaim 29, wherein the command dispatcher is configured to process thenumber of commands in response to a respective channel buffer of atleast one of the plurality of back end channels being full.
 31. Thesolid state drive of claim 29, wherein the command dispatcher isconfigured to optimize distribution of the number of commands bycombining at least two commands of the number of commands in response todetermining that the at least two commands of the number of commands arefor a same operation.
 32. The solid state drive of claim 31, wherein theat least two commands of the number of commands involve two or morelogically overlapping memory locations.
 33. The solid state drive ofclaim 31, wherein the at least two commands of the number of commandsinvolve two or more logically adjacent memory locations.
 34. The solidstate drive of claim 32, wherein the two or more logically adjacentmemory locations are associated with a same back end channel.
 35. Amethod, comprising: receiving a number of commands from a command queuein an order; processing the number of commands to optimize adistribution of the number of commands among a plurality of back endchannels; and processing a respective payload associated with the numbercommands.
 36. The method of claim 35, wherein the number of commandsinvolve more than one of the plurality of back end channels.
 37. Themethod of claim 35, comprising processing the number of commands tooptimize their distribution based on the number of commands held in thecommand queue.
 38. The method of claim 35, comprising processing thenumber of commands on a front end of a memory controller to optimizetheir distribution to a back end of the controller by selectivelyreordering commands, selectively combining commands, and/or selectivelydeleting commands.
 39. The method of claim 35, comprising configuringeach of the plurality of back end channels to further processrespectively received commands by selectively modifying the number ofcommands to expedite execution of the number of commands.
 40. The methodof 39, wherein modifying the number of commands includes selectivelyreordering received commands, selectively combining received commands,and/or selectively deleting received commands.